IAP oligonucleotide probes derived from expressed IAP proviral elements detect restriction fragments which have characteristic strain distribution patterns (SDPs) among different strains of mice, making them suitable multilocus probes for genome mapping. Chromosomal assignments for 47 IAP loci were made in the A/J X C57BL/6J (AXB BXA) recombinant inbred (RI) strains. These included 27 previously unmapped loci in the A strain. Forty-six IAP loci were mapped in the C57BL/6 X C3H (BXH) RI set. The 20 IAP loci in the H strain provided new markers that had not been previously mapped. Mapping of IAP loci in the BALB/c strain was done using somatic cell hybrids, and the BALB/c X S/J (BXS) and C57BL/6 X BALB/c (CXB) RI panels. This mapping led to identification of a number of chromosomal regions carrying Iapls loci that are commonly hypomethylated in plasmacytomas, B-cell tumors, and myeloid tumors in BALB/c mice. These regions included distal chromosome (Chr) 2, distal Chr 4, proximal and distal Chr 7.